1. Field of the Invention
The present invention relates to a polarized light synthesizing device for synthesizing two linearly polarized lights which are mutually different in polarization plane, and a display device using the same.
2. Description of the Related Art
As a display device capable of displaying an image on a screen with a large image plane, there has been developed a so-called light valve display device. Recently, of this type light valve display device, there is watched a liquid crystal light valve device which is capable of implementing a high resolution, and is independent of magnetism.
The liquid crystal light valve device is basically arranged in such a manner that light from a light source is applied to a liquid crystal panel, and transmitted light, according to an image formed on the liquid crystal panel, is introduced onto a screen with an enlargement, so that a large image plane of the image is displayed. In this case, the liquid crystal panel forms an image using a polarizer and an optical change by the dielectric anisotropy of the liquid crystal. When light from the light source is converted into linearly polarized light by the polarizer, the half of it is lost.
In view of the foregoing, there is proposed a liquid crystal light valve display device 4 (FIG. 18) using a polarized light synthesizer device 2 shown in FIG. 17 (Japanese Patent Application Laid-Open Gazette Hei.4-310903). According to the liquid crystal light valve display device 4, after light L from a light source 6 is introduced via an aperture member 8 into a condenser lens 10 to form a parallel luminous flux, the parallel luminous flux is converted into the linearly polarized light by the polarized light synthesizer device 2 and then introduced to a liquid crystal panel 12. The linearly polarized light introduced to the liquid crystal panel 12 penetrates a polarizer 14 disposed at the front stage of the liquid crystal panel 12, selectively penetrates a liquid crystal 18 controlled in accordance with an image signal generated from a liquid crystal control unit 16, penetrates a polarizer 20 disposed at the back stage of the liquid crystal panel 12, and is introduced via condenser lenses 22 and 24 into a screen 26 thereby displaying a large image plane of image.
Here, the polarized light synthesizer device 2 is arranged in such a manner that a lenticular lens 30, in which a plurality of semi-columnar convex lenses are arranged, is disposed at the incident side of a polarization panel 28 for converting the light L into the linearly polarized light, while a plurality of line-like shaped phase difference plates 32 associated with coupling portions of the plurality of semi-columnar convex lenses constituting the lenticular lens 30 are disposed at the emission side of the polarization panel 28. Incidentally, a direction of a slanting line appended to the polarization panel 28 denotes a superposing direction of a plurality of polarization separation working films.
In this case, the light L consisting of the parallel luminous flux introduced by the polarized light synthesizer device 2 is concentrated by lenticular lens 30, and then separated by the polarization panel 28 into two linearly polarized lights which are perpendicularly intersect one another in the polarization plane. One of the two linearly polarized lights is introduced to the liquid crystal panel 12 through slits between the phase difference plates 32. Another of the two linearly polarized lights is introduced to the liquid crystal panel 12 through the phase difference plates 32 in the form of a linearly polarized light having the polarization direction which is the same as that of said one of the linearly polarized lights. Incidentally, in FIG. 17, the symbol marks ".largecircle. and .cndot." and the symbol mark of the both direction arrow denote a direction perpendicularly intersecting the drawing and a polarization plane of the direction along the drawing, respectively.
The light L, which penetrates the polarized light synthesizer device 2 thus arranged, reaches a liquid crystal 18 constituting liquid crystal panel 12 in the form of the linearly polarized light controlled to the polarization plane of the same direction as the polarizer 14, and thereafter be introduced to the polarizer 20 selectively penetrating the liquid crystal 18 in accordance with an image.
However, since the polarization panel 28 constituting the polarized light synthesizer device 2 is formed by superposing a plurality of polarization separation working films, a change of incident angle of light L with respect to the superposing plane may bring about a remarkable degradation of a polarization separation characteristic. Consequently, there is a need to supply to the polarized light synthesizer device 2 a parallel luminous flux which is strictly controlled in parallelism. This causes the fabrication cost of the polarization panel 28 to rise. Further, the polarized light synthesizer device 2 has to be constructed with the same size as the liquid crystal panel 12. This causes the device to be large and thereby further increasing the cost.